SELECT 
  p.product_id, 
  ifnull(
    count(dp.post_id), 
    0
  ) as discussion_amount_posts 
FROM 
  cscart_discussion 
  INNER JOIN cscart_products as p ON (
    cscart_discussion.object_id = p.product_id
  ) 
  INNER JOIN cscart_discussion_posts as dp ON (
    cscart_discussion.thread_id = dp.thread_id 
    AND cscart_discussion.object_type = 'P' 
    AND cscart_discussion.company_id = 1
  ) 
WHERE 
  dp.status = 'A' 
  and p.product_id in (
    51232, 12, 51238, 51237, 51236, 51235, 
    51234, 51233, 51289, 51288, 51287, 
    51286, 51285, 51284, 51283, 8, 56, 81, 
    11, 4, 51361, 30, 51362, 51363, 51364, 
    51365, 31, 51366, 51367, 51368, 51369, 
    46, 51370, 51371, 51372, 51373, 51452, 
    51453
  ) 
GROUP BY 
  p.product_id

Query time 0.00062

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}